Variable volume safe and arm mechanism

ABSTRACT

A safe and arm mechanism is provided employing in combination a pressure-responsive diaphragm and a variable volume chamber which are adaptable to change the mechanism from the &#39;&#39;&#39;&#39;safe&#39;&#39;&#39;&#39; configuration to the &#39;&#39;&#39;&#39;armed&#39;&#39;&#39;&#39; configuration. In the &#39;&#39;&#39;&#39;safe&#39;&#39;&#39;&#39; configuration gas pressure resulting from accidental ignition of a squib is insufficient to rupture the pressure-responsive diaphragm protecting the device in which the safe and arm mechanism is employed. In the &#39;&#39;&#39;&#39;armed&#39;&#39;&#39;&#39; configuration the available volume of the variable volume chamber is reduced and ignition of a squib within the mechanism ruptures the pressureresponsive diaphragm allowing the squib gases to initiate an igniter.

D United States Patent n 1 3,577,926

[72] Inventor Wilfred C. Schuemann 3,343,489 9/1967 Whitehouse 102/76 2 I l A I No 325 Primary Examiner-Benjamin A. Borchelt Assistant Examiner-Thomas H. Webb Wed 1968 Attorney-William F Smith (45] Patented May 11, 1971 [73] Assignee Hercules, Incorporated Wilmington, Del.

[54] VARIABLE VOLUME SAFE AND ARM {\BS TRACT: A safe and arm mechanism is provided employ- MECHANISM mg m combination a pressure-responsive diaphragm and a 7 Claims, 4 Drawing Figs. variable volume chamber which are adaptable to change the mechanism from the safe configuration to the armedl U.S. configuration In the safe' configuration gas pressure result- [5 l [Ill- Cl from accidental ignition fa is insufficient to rupture [50] F M f h F420 F4261 the pressure-responsive diaphragm protecting the device in le 0 Scale the safe and arm mechanism is employed In the ar. med" configuration the available volume of the variable [56] References cited volume chamber is reduced and ignition of a squib within the UNITED STATES PATENTS mechanism ruptures the pressure-responsive diaphragm al- 2,939,393 6/ 1960 Johnson et al. 102/76 lowing the squib gases to initiate an igniter.

3O -l4 26 32 22 l Patented May 11, 1971 FIG. 2

FIG.

FIG.3

WILFRED C. SCHUEMANN INVENTOR BY my ATTORNEY VARIABLE VOLUME SAFE AND ARM MECHANISM This invention relates to a variable volume safe and arm mechanism for use in munitions, missiles, and rockets.

In an explosive device, it is desirable for safety purposes to employ some mechanism for isolating the squib, the primary initiator in an explosive train containing highly sensitive explosive ingredients, from the next element in the explosive train referred to hereinafter as the igniter, until such time as it is desired to arm" the igniter. The device or mechanism employed to accomplish this result is commonly referred to as a safe and arm mechanism. A safe and arm mechanism when in a safe" configuration, isolates the squib from the igniter. Accidental ignition of the squib in a device protected with a safe and arm mechanism will not initiate the igniter. When in an armed configuration, however, flame and hot gases resulting from intentional initiation of the squib are transmitted directly to the igniter for its ignition.

Most safe and arm mechanisms currently in use employ some type of a diverter shaft which rotates or moves into and out of position in a connecting conduit between the squib and igniter depending on whether the squib is to be isolated or communicatively connected to the igniter. In the safe position the diverter shaft blocks the conduit connecting the squib to the igniter so as to divert the output from an ignited squib away from the igniter, usually into a free volume. ln the armed configuration the diverter shaft is moved so as to block the conduit to the free volume leaving the conduit to the igniter open. The inherent difficulty with this type of safe and arm mechanism is in making a reliable seal between the diverter shaft and the conduit connecting the squib and igniter when the mechanism is in the safe position. lf the squib is accidentally fired with this safe and arm mechanism in the safe position, any failure of the seal due to improper machining, careless assembly, wear or dirt can allow passage of sufficient flame and hot gases past the seal to initiate the igniter. To prevent such problems, seals must be made of complex design, requiring close tolerances of parts, and having high-quality surface finishes. Such seals are very expensive. Additional problems with this type of safe and arm mechanism result from the necessity to employ O-ring seals to seal various openings in the conduits required for operation of the diverter shaft.

The complex design of prior art safe and arm mechanisms heretofore generally described necessarily results in a relatively long connecting conduit between the squib and igniter. The length of this connecting conduit is determinative of the output energy of the squib required to insure reliable ignition of the igniter, the output energy of the squib increasing with increasing length of the conduit. Production of high output energy squibs required because of this long connecting conduit is very difficult since uniform output characteristics of high output energy squibs is difficult to maintain but is a definite necessity.

lt is the principal object of this invention to provide a safe and arm mechanism that eliminates the necessity of a diverter shaft and its inherent deficiencies in safe and arm mechanisms heretofore described.

it is another object of this invention to provide a highly reliable low-cost safe and arm device for munitions.

It is still another object of this invention to provide a safe and arm mechanism not requiring high output energy squibs for reliable operation.

Other objects of this invention will in part be obvious and will in part appear hereinafter. For a more complete understanding of the nature and objects of this invention, reference is made to the following detailed description taken in connection with the accompanying drawings.

FIG. I is a longitudinal view partially in section of an embodiment of a variable-volume safe and arm device of this invention in the safe position.

FIG. 2 is a longitudinal view partly in section of the variablevolume safe and arm device of HO. 1 in the armed position.

FIG. 3 is a longitudinal view of another embodiment partly in section of a variable-volume safe and arm device in the safe position.

FIG. 4 is a longitudinal view of the variable-volume safe and arm device of F IG. 3 in the armed position.

In FlG. 1 a variable-volume safe and arm mechanism is shown in the safe" configuration. The safe and arm mechanism is comprised of a chamber body 10 having a freevolume cavity 12 and a squib cavity 14. A first connecting conduit 16 communicates the free-volume cavity 12 with a squib 18 which is secured within the squib cavity 14. A first pressure-responsive means, such as diaphragm 20, is placed across the first connecting conduit 16 and separates the free volume of the free-volume cavity 12 from squib 18. A second connecting conduit 22 communicates the squib 18 with an ig niter 24 (not shown). A second pressure-responsive means, such as diaphragm 26 is placed in connecting conduit 22 and separates the squib 18 from the igniter 24. A diaphragm support piston 28 is shown passing through a cavity 30 in chamber body 10. The diaphragm support piston 28 is shown in the inoperative position with the free-volume cavity 12in direct communication with the diaphragm 20. Diaphragm 20 is in a nonsupported configuration and has a lower rupture pressure than the diaphragm 26. If accidental ignition of squib l8'takes place such as by a stray current passing through a bridgewire 32 in the squib l8, diaphragm 20 will rupture relieving the pressure resulting from burning of the squib composition through connecting conduit 16 into free-volume cavity 12 so that the pressure on diaphragm 26 is below its rupture pressure at all times.

In FIG. 2 the variable-volume safe and arm device of FIG. 1 is shown in the armed" position. In this position the diaphragm support piston 28 is shown moved into an operative position 34 directly behind diaphragm 20. In the operative position 34, the diaphragm support piston 28 isolates the free volume of the free-volume cavity 12 from the squib l8 and increases the rupture pressure of diaphragm 20 to a value substantially above the rupture pressure of diaphragm 26. If squib 18 is initiated while the safe and arm mechanism is in the armed position as described, the pressure resulting from burning of the squib composition ruptures diaphragm 26 andignites theigniter 24. The diaphragm support piston 28 can be moved into operative position 34 by electrical and mechanical means (not shown). Methods for moving the piston common to the munitions art such as for example, spin, setback, or deceleration systems could be readily adapted for moving the diaphragm support piston 28 into operative position 34, as those skilled in the art will clearly understand.

In FIG. 3 another embodiment of a variable-volume safe and arm mechanism is shown in the safeconfiguration. The safe and arm mechanism is comprised of a chamber body 36 having a free-volume cavity 38 adaptable to receive a piston. A piston 40 is shown positioned in the free-volume cavity in an inoperative position which provides available free-volume 42 forward of the forward end 44 of piston 40. The piston 40 is slidably movable into the free-volume cavity 38 and has a squib cavity 46 in its forward end 44. A squib 48 is secured within squib cavity 46. A connecting conduit 50 communicates the squib 48 with the igniter 52 (not shown). A pressure-responsive diaphragm 54 secured within connecting conduit 50 separates the igniter 52 from the squib 48.

The available free volume 42 of the free-volume cavity 38 is communicatively connected to the squib 48through conduit 56 which is also a part of conduit 50. If accidental ignition of squib 48 takes place such as by a stray current passing through bridgewire 58 in squib 48, the hot gases resulting from combustion of the squib explosive composition will be contained within the total available volume of the safe and arm mechanism, comprised of available free volume 42 and the volume of the connecting conduit. The resulting pressure within the safe and arm mechanism will be less than the rupture pressure of diaphragm 54.

In FIG. 4 the safe and arm mechanism of FIG. 3 is shown in the armed position. In this position piston 40 is moved forward into operative position 60 in free-volume cavity 38 substantially isolating free volume from squib 48. In the operative position 60 the squib 48 is in communicating relationship with diaphragm 54 through conduit 50. When squib 48 is fired by a suitable means such as by electric current passing through bridgewire 58, the pressure resulting from combustion of the squib explosive composition ruptures diaphragm 54 since the volume into which the gases are released is substantially reduced when the safe and arm mechanism is in the "armed position. Hot-buming gasses from the ignited squib flow past ruptured diaphragm 54 and initiate igniter 52.

The simple design of this safe and arm mechanism is based on tailoring a squib output, i.'e., the volume of gases generated upon initiation of the squib to the total available volume of the safe and arm mechanism into which these gases can be directed and to the rupturing pressure of the pressure-responsive diaphragms employed. Numerous methods of securing pressure responsive diaphragms within the safe and arm mechanism described are satisfactory such as adhesive bonding, welding and compression fitting. All types of pressureresponsive diaphragms or rupture discs can be employed.

lclaim:

1. ln a safe and arm mechanism for preventing accidental ignition of an igniter, said safe and arm mechanism comprising a chamber body having a free-volume cavity and a squib, the improvement comprising:

a. a first conduit means communicatively connecting the squib and the igniter,

b. a pressure-responsive means secured within said first conduit means isolating the igniter from the squib,

c. a second conduit means communicatively connecting the squib and the free-volume cavity,

d. an element movable into the free-volume cavity having an inoperative position in which the free volume of freevolume cavity and squib are communicatively connected through the second conduit means resulting in the safe and arm mechanism being in a safe" position, and having an operative position in which movable element isolates the free volume of the free-volume cavity from the squib resulting in the safe and arm mechanism being in an armed position, and

e. means for moving said movable element from the inoperative position to the operative position.

2. The safe and arm mechanism of claim I in which the pressure-responsive means is a diaphragm.

3. The safe and arm mechanism of claim 2 in which the movable element is a piston.

4. In a safe and arm mechanism for preventing accidental ignition of an igniter comprising a chamber body having a freevolume cavity, a squib cavity, and a squib secured within said squib cavity, the improvement comprising:

a. a first conduit means communicatively connecting the squib and the igniterr b. a first pressure-responsive means secured within said first conduit means for isolating the igniter from the squib,

c. a second conduit means communicatively connecting the squib and the free-volume cavity,

d. a second pressure-responsive means secured with said second conduit means having a lower rupture pressure than said first pressure-responsive means and separating the free-volume cavity from the squib,

e. an element movable into the free-volume cavity having an inoperative position in which the free volume of the freevolume cavity and the squib are separated by the second pressure responsive means and having an armed position in which the movable element isolates the free volume of the free-volume cavity from the second pressure-responsive means and provides support for the second pressureresponsive means whereby its rupture pressure is increased over the rupture pressure of the first pressureresponsive means, and f. means for moving said movable element from the inoperative position to the operative position.

5. The safe and arm mechanism of claim 4 wherein the first and second pressure responsive means are rupture diaphragrns, and the element movable into the free-volume cavity is a piston.

6. In a safe and arm mechanism for preventing accidental ignition of an igniter, said safe and arm mechanism comprising a chamber body having a free-volume cavity and a squib, the improvement comprising:

a. a piston slidably movable into said free-volume cavity,

said piston having a squib cavity,

b. the squib secured within said squib cavity,

c. a first conduit means communicatively connecting the squib and the igniter,

d. a pressure-responsive means secured within said first conduit means isolating the igniter from the squib,

e. a second conduit means communicatively connecting the squib and the free-volume cavity, and

f means for moving said piston from an inoperative position in which the free volume of the free-volume cavity and squib are communicatively connected and in which the safe and arm mechanism is in a safe position, to an operative position in which the free volume of the free-volume cavity is isolated from the squib and in which the safe and arm mechanism is in an anned position.

7. The safe and arm mechanism of claim 6 in which the pressure-responsive means is a diaphragm. 

1. In a safe and arm mechanism for preventing accidental ignition of an igniter, said safe and arm mechanism comprising a chamber body having a free-volume cavity and a squib, the improvement comprising: a. a first conduit means communicatively connecting the squib and the igniter, b. a pressure-responsive means secured within said first conduit means isolating the igniter from the squib, c. a second conduit means communicatively connecting the squib and the free-volume cavity, d. an element movable into the free-volume cavity having an inoperative position in which the free volume of free-volume cavity and squib are communicatively connected through the second conduit means resulting in the safe and arm mechanism being in a ''''safe'''' position, and having an operative position in which movable element isolates the free volume of the freevolume cavity from the squib resulting in the safe and arm mechanism being in an armed position, and e. means for moving said movable element from the inoperative position to the operative position.
 2. The safe and arm mechanism of claim 1 in which the pressure-responsive means is a diaphragm.
 3. The safe and arm mechanism of claim 2 in which the movable element is a piston.
 4. In a safe and arm mechanism for preventing accidental ignition of an igniter comprising a chamber body having a free-volume cavity, a squib cavity, and a squib secured within said squib cavity, the improvement comprising: a. a first conduit means communicatively connecting the squib and the igniter. b. a first pressure-responsive means secured within said first conduit means for isolating the igniter from the squib, c. a second conduit means communicatively connecting the squib and the free-volume cavity, d. a second pressure-responsive means secured with said second conduit means having a lower rupture pressure than said first pressure-responsive means and separating the free-volume cavity from the squib, e. an element movable into the free-volume cavity having an inoperative position in which the free volume of the free-volume cavity and the squib are separated by the second pressure responsive means and having an armed position in which the movable element isolates the free volume of the free-volume cavity from the second pressure-responsive means and provides support for the second pressure-responsive means whereby its rupture pressure is increased over the rupture pressure of the first pressure-responsive means, and f. means for moving said movable element from the inoperative position to the operative position.
 5. The safe and arm mechanism of claim 4 wherein the first and second pressure responsive means are rupture diaphragms, and the element movable into the free-volume cavity is a piston.
 6. In a safe and arm mechanism for preventing accidental ignition of an igniter, said safe and arm mechanism comprising a chamber body having a free-volume cavity and a squib, the improvement comprising: a. a piston slidably movable into said free-volume cavity, said piston having a squib cavity, b. the squib secured within said squib cavity, c. a first conduit means communicatively connecting the squib and the igniter, d. a pressure-responsive means secured within said first conduit means isolating the igniter from the squib, e. a second conduit means communicatively connecting the squib and the free-volume cavity, and f. means for moving said piston from an inoperative position in which the free volume of the free-volume cavity and squib are communicatively connected and in which the safe and arm mechanism is in a safe position, to an operative position in which the free volume of the free-volume cavity is isolated from the squib and in which the safe and arm mechanism is in an armed position.
 7. The safe and arm mechanism of claim 6 in which the pressure-responsive means is a diaphragm. 